A Bolt of Brilliance: Harvesting "Pee Power"

With the help of bugs, human urine and even sweat can be used to generate electricity. Waste-water treatment could be an early application, reports Lee Williams

It is a mark of the popularity of the Glastonbury Festival – and perhaps the amount drunk there – that this year just one urinal had to deal with up to 1,000 litres of urine a day.

But this toilet, located near the Pyramid Stage, was different from the others. All that pee wasn’t just flushed away but instead converted into electricity which was used to power message boards providing festival updates.

The 40-person Pee Power urinal, developed by scientists from the University of the West of England (UWE) in Bristol, uses bacteria to convert chemical energy in the urine into electricity.

“It’s essentially the same principle as any other chemical fuel cell,” says Ioannis Ieropoulos, who leads the research at UWE. These microbial fuel cells (MFCs) comprise an anode and a cathode, which generate a flow of electrons, but, instead of using expensive materials, the cells contain micro-organisms that break down the organic compounds within the urine to produce a current.

“The microbes donate electrons,” explains Ieropoulos, “because to them it’s a by-product of their anaerobic respiration that they need to get rid of.” The bugs themselves aren’t particularly special – UWE gets them from sludge donated by the local water company. They are a type of bacteria known as electroactive micro-organisms that have the special ability of being able to transfer electrons produced within their cells to an external receptor such as an anode.

One of the Glastonbury festivals, held in Somerset, England (Credit: iStock)
The cheap option

Microbial fuel cells have been known about for some time but what is making them more relevant in an increasingly energy-conscious world – and why they now have their own stage at Glastonbury – is that they are very cheap, and very renewable. They use carbon electrodes, so expensive metals aren’t necessary; the bacteria are common and free and the fuel itself is everywhere.

“You can use anything that contains organics. You can use urine or any type of waste water because that is the food for these bacteria,” explains Mirella Di Lorenzo, who heads a research team developing its own biofuel cells using urine and other bodily fluids at the University of Bath.

And that’s not their only advantage. Not only do microbial fuel cells generate electricity inexpensively from waste water, they can also clean the water in the process. This is because the electroactive micro-organisms break down and consume the long-chain sugars found in the waste water, effectively removing chemicals such as carbon, nitrogen, phosphorous, potassium, magnesium and sodium from the water – a very similar process to what happens in waste-water treatment plants.

Part of the Pee Power project at Glastonbury was to analyse the waste water, collected in fridges next to the urinal, to see just how much cleaning had taken place. So far, according to Ieropoulos, the team has achieved purity levels of 90-95% in lab conditions and 60% in field conditions. “It’s not clean to potable levels,” he says, “but that’s something we’re seriously looking at.”

Ieropoulos’s team has already considered using MFCs to power robots which could find their own food, digest it, and get rid of their own (clean) waste. Now, with projects such as Pee Power, they are looking at providing lighting for so-called ‘smart toilets’ that can also offer recharging points for mobile phones.

And they want to take the idea even further. Backed by Oxfam, the researchers are trying to find ways to provide facilities for rural communities and refugee camps in the developing world. They are also looking into a wearable device that could be used by hikers, divers, soldiers or even astronauts that would use the wearer’s urine to power a beacon signal in case of emergencies.

Sweat and radio waves

But it isn’t just the diversity of applications that makes biofuel cells exciting – it is the range of fuels themselves, which can include pretty much anything secreted by the body. A team from the University of California, San Diego (UCSD) has exploited this by extracting energy from sweat. They showed in a recent experiment that they could generate enough current to power a Bluetooth radio.

The UCSD device works by using enzymes to convert the lactate found in sweat into electricity. The benefit of using enzymes instead of microbes is greater efficiency, according to Amay Bandodkar, a chemist at the UCSD. “If we can use enzymes directly,” he says, “we can get rid of all the extra resistive material of the body of the microbes and just use the enzymes for producing the current.”

Researchers Jon Chouler and Mirella Di Lorenzo with lecturer Petra Cameron test the microbial fuel cell (Credit: University of Bath)
Powering up for the future

The other way the team has produced extra power – around a milliwatt per cm2 – is by placing the biofuel cells within three-dimensional carbon nanotubes, set on island-like structures connected by springy bridges. This island-bridge structure is laminated onto a stretchable polymer material that connects to the skin as a small wearable patch. This gives the patch the softness and stretchability to attach to the skin, without compromising the efficiency of the biofuel cells. The structure has allowed the cells to generate 10 times more power than previous attempts – enough for someone to charge a mobile device while jogging.

But the team isn’t satisfied with what they have achieved. Their aim is to amp up the power even more, enough to provide a versatile wearable device that could power a wide range of different sensors.

The only thing standing in their way – as with other biofuel cells – is power. Biofuel cells by their very nature are tiny. They can only generate electricity on the scale of micro and milliwatts and will never solve our energy problems alone, says Di Lorenzo. However, it doesn’t mean they can’t achieve big things. Ieropoulos’s Pee Power system, where the MFCs are arranged in stacks (essentially like connecting cells in series), has recently achieved a full watt of power.

Ieropoulos sees a long-term future where MFCs are used to treat waste water while also providing useful amounts of energy. “The energy content of municipal waste water is actually more than what a waste-water treatment plant is consuming,” he says. “We are looking at a future where waste-water treatment plants are actually power stations. They treat the waste water but at the same time cover their own energy consumption and even provide excess energy back to the grid.”

And Di Lorenzo agrees that biofuel cells will be an important part of our future energy solutions. “Biofuel cells are a technology that is extremely inexpensive and that generates electricity from waste,” she says. “At the moment we have nothing else like that. They have too many benefits to be ignored.”